As known, light emitting diodes (LEDs) have many benefits such as high luminance, lower power consumption and long service life. Consequently, light emitting diodes have been widely used in general instruments, indicating lamps or lighting devices. In case that light emitting diodes are applied to a lighting device, the lighting device usually comprises a lighting module. The lighting module comprises plural light emitting diodes that are connected with each other in series or in parallel. Consequently, the light beams emitted by the lighting device have large coverage range and high brightness.
FIG. 1A is a schematic perspective view illustrating a portion of a conventional linear LED lighting device. As shown in FIG. 1A, the conventional linear LED lighting device 1 comprises a lampshade 10 and a LED module 11 (see FIG. 1B). The LED module 11 is covered by the lampshade 10. The lampshade 10 is made of a transparent material. Moreover, plural textured structures (not shown) are formed on a surface of the lampshade 10, and a diffuser (not shown) is disposed within the lampshade 10. Due to the textured structures and the diffuser, a desired light pattern is produced.
As shown in FIG. 1A, the lampshade 10 has a linear tube profile with a hollow square cross section. Please refer to FIG. 1B. FIG. 1B schematically illustrates some simulated light patterns generated by the conventional linear LED lighting device of FIG. 1A. As shown in FIG. 1B, the LED module 11 is disposed within the lampshade 10. The LED module 11 comprises plural light emitting diodes (not shown), and the plural light emitting diodes are arranged in a line. Moreover, the linear LED lighting device is equipped with optical elements (e.g., lenses) as a diffuser. By the LED module 11, the diffuser and the lampshade 10, the desired light pattern is produced.
In FIG. 1B, three light patterns (a), (b) and (c) are shown. These light patterns (a), (b) and (c) are produced by three linear LED lighting devices 1, 1′ and 1″, respectively. The linear LED lighting device 1 comprises a lampshade 10 or a corresponding diffuser. The linear LED lighting device 1′ comprises a lampshade 10′ or a corresponding diffuser. The linear LED lighting device 1″ comprises a lampshade 10″ or a corresponding diffuser. The lampshades 10, 10′ and 10″ have different textured structures or different type of diffusers. In the light pattern (a), the light intensity on periphery region is stronger and the light intensity on the middle region is weaker. In the light pattern (b), the light intensity is centralized to the middle region. In the light pattern (c), the light intensity in the coverage region of the light beams is uniform. In the light pattern (a), (b) or (c), the coverage range of the light beams is mainly located under the linear LED lighting device. Due to the angular limitations, the luminous efficiency is usually unsatisfied. Moreover, since the lampshade has special textured structures or an additional diffuser is needed, the fabricating cost of the conventional linear LED lighting device is high.
FIG. 2A is a schematic perspective view illustrating the outer appearance of another conventional linear LED lighting device. As shown in FIG. 2A, the conventional linear LED lighting device 2 comprises a lampshade 20 and a LED module 21. The LED module 21 is arranged in a line. The lampshade 20 has a linear tube profile with a hollow circular cross section. The lampshade 20 is made of a translucent material. Consequently, the lampshade 20 is a hazy lampshade. Since the hazy lampshade has the curvy surface, the light beams from the LED module 21 are scattered more uniformly. Under this circumstance, it is not necessary to use an additional diffuser. In comparison with the linear LED lighting device 1 of FIG. 1A, the fabricating cost of the linear LED lighting device 2 is lower. FIG. 2B is a diagram showing a simulated light intensity distribution generated by the conventional linear LED lighting device of FIG. 2A. As shown in FIG. 2B, the linear LED lighting device 2 produces a circular light pattern. The circular light pattern is advantageous because of the optical uniformity. However, the linear LED lighting device 2 cannot emit the light beams in a wide-angle illumination manner or at a specified illumination angle. That is, the applications are limited.
Therefore, there is a need of providing a wide-angle linear LED lighting device in order to solve the above drawbacks.